Upgrading to asset pipeline could be a big change and break those deploymnts who are already using it with resources. I am thinking wht can we do. Seriously i personally dont like asset pipeline, there are some limitations, like css / js cant be specified in same bundle, bundling cant be disabled in production etc, but if resources is not going to be maintained, we will have to replace

by putting the right manifests in the assets directory it is possible to support both as assets-pipeline will look in the web-app folder as well as the assets folder.

it took me two days, but that included a whole bunch of other stuff.
the hard part it getting bootstrap right. note that i have previously upgraded to bootstrap3

in my app i use:
mordernizr/js-webshim to support IE8 (which i have to do)
metisMenu for an sidebar accordian menu
maritup, bootstrap-checkbox, bootstrap-select, bootstrap-validator and select2 for various UI components

my application.js file is:

//= require modernizr/modernizr-2.7.1.js
//= require js-webshim/dev/polyfiller.js
//= require js-webshim/webshim.js
//= require jquery.js
//= require bootstrap/js/affix.js
//= require bootstrap/js/alert.js
//= require bootstrap/js/button.js
//= require bootstrap/js/carousel.js
//= require bootstrap/js/collapse.js
//= require bootstrap/js/dropdown.js
//= require bootstrap/js/modal.js
//= require bootstrap/js/tooltip.js
//= require bootstrap/js/popover.js
//= require bootstrap/js/scrollspy.js
//= require bootstrap/js/tab.js
//= require bootstrap/js/transition.js
//= require metisMenu/metisMenu.js
//= require sidebar.js
//= require bootstrap-checkbox/js/checkbox-x.js
//= require bootstrap-select/js/bootstrap-select.js
//= require bootstrap-validator/js/bootstrapValidator.js
//= require select2/select2.js
//= require MarkItUp/markitup/jquery.markitup.js
//= require MarkItUp/markitup/sets/html/set.js
//= require jquery-jgrowl/jquery.jgrowl.js
//= require jquery-pwstrength-bootstrap/pwstrength-bootstrap-1.2.2.js
//= require nimble.ui.js
//= require nimble.core.js

i use bootswatch to provide my bootstrap theme.
i copied font-awesome into my assets directory becuase i could not get the plugn to play nicely.

my application.css file is:

*= require bootswatch/${grails.util.Holders.getGrailsApplication().config.theme}/theme.less
*= require metisMenu/metisMenu.css
*= require sidebar/sidebar.less
*= require bootstrap-checkbox/css/checkbox-x.css
*= require bootstrap-select/css/bootstrap-select.css
*= require bootstrap-validator/css/bootstrapValidator.css
*= require select2/select2.css
*= require select2-bootstrap3.css
*= require MarkItUp/markitup/skins/markitup/style.css
*= require MarkItUp/markitup/sets/html/style.css
*= require font-awesome.css